Echocardiographic assessment of the right heart

INTRODUCTION — The right ventricle (RV) has historically received less attention than its counterpart of the left side of the heart, yet there is a substantial body of evidence showing that RV size and function are perhaps equally important in predicting adverse outcomes in cardiovascular disease. RV dysfunction is associated with excess morbidity and mortality in patients with chronic left-sided heart failure, acute myocardial infarction (with or without RV involvement), pulmonary embolism, pulmonary arterial hypertension, and congenital heart disease. Advances in noninvasive imaging of the RV, particularly with echocardiography, have yielded insights into the pathophysiology of this complex and once elusive chamber.

In an attempt to standardize the echocardiographic evaluation of the right heart, the American Society of Echocardiography published guidelines on measures and normal reference values to identify right ventricular pathology   and the American Society of Echocardiography and European Association of Cardiovascular Imaging (ASE/EACVI) subsequently updated some of these reference values. This topic will review the echocardiographic assessment of the right heart, specifically the right atrium (RA) and RV.

RIGHT VENTRICULAR ANATOMY AND PHYSIOLOGY — The right atrium (RA) transmits and pumps blood across the tricuspid valve into the right ventricle (RV), which then ejects the stroke volume through the pulmonic valve and into the main pulmonary artery. In the absence of shunt, forward stroke volume of the right heart is obligately equal to that of the left.

The right heart differs from the left in terms of anatomy and physiology. The RV loosely resembles a pyramid and is composed of three portions: the inlet, the body, and the outflow tract. Contraction is generated by a deep layer of longitudinal fibers that result in longitudinal (base to apex) shortening, and a superficial layer of circumferential fibers that result in inward thickening. The RV lacks a third layer of spiral fibers as seen in the left ventricle.

The RV end-diastolic volume is slightly larger than that of the left ventricle, and as a result has a slightly lower ejection fraction. RV ejection is accomplished with a mass that is approximately one-fifth that of the left ventricle. Accordingly, the RV is well suited as a volume pump, but is prone to failure when faced with an acute pressure challenge.

These anatomic and physiologic features, coupled with the less accessible retrosternal position of the RV, have resulted in many challenges in the noninvasive evaluation of RV size and function by echocardiography.

CHAMBER SIZE AND WALL THICKNESS — Certain descriptive features may raise the suspicion of right-sided pathology. As an example, the right ventricular (RV) cavity size may be described as “as large as” (suggestive of moderate dilation) or “larger than” (suggestive of severe dilation) the left ventricle in the apical four-chamber view, or the RV may be described as “apex-forming” (suggestive of significant dilation). However, given the complex and multifaceted configuration of the RV, all available echocardiographic views should be reviewed to obtain a comprehensive assessment, and quantitative measures of RV and right atrium (RA) size and function should be reported as part of a comprehensive echocardiographic assessment.

Right atrial size — Emerging data have suggested that RA enlargement is an important prognostic marker for patients with various types of cardiopulmonary disease, which should be routinely measured in the echocardiography lab.

●In a study of 81 patients with primary pulmonary hypertension followed for an average of 37 months, RA area indexed to height was one of only two echocardiographic predictors of mortality .

●In a study of 192 patients with chronic systolic heart failure followed for an average of 36 months, RA volume indexed to body surface area (BSA) was found to be predictive of mortality, need for heart transplantation, or hospitalization for heart failure; an association that persisted after adjusting for age, left ventricular ejection fraction, RV systolic function, and brain natriuretic peptide (BNP).

●Atrial fibrillation and flutter may originate from electrophysiologic perturbations within the RA, and RA enlargement has been shown to be a risk factor for the development of these arrhythmias .

RA area — RA area is measured by planimetry of the RA cavity in the apical four chamber view at end-systole (when the RA cavity is at its largest).

Right atrial (RA) area (shown in yellow) is measured by planimetry of the atrial cavity in the apical four chamber view at end-systole (when the atrial cavity is at its largest). RA linear dimensions can also be measured in the apical four chamber view at end-systole. The normal reference limits for RA major-axis dimension (superior-inferior, from the center of the tricuspid annular plane to the uppermost aspect of the RA wall, shown as line 1) and minor-axis dimension (left-right, from the interatrial septum to the rightmost aspect of the RA wall, shown as line 2) are ≤5.3 cm and ≤4.4 cm, respectively.

When tracing the endocardial contour, the area below the tricuspid annular plane, the superior and inferior vena cava, and the RA appendage should be excluded. The normal reference limit for RA area is ≤18 cm2. Of note, RA volume (see below) has supplanted RA area as the preferred measure.

RA linear dimensions — RA linear dimensions can also be measured in the apical four chamber view at end-systole. The normal reference limits for RA major-axis dimension indexed to BSA (superior-inferior, from the center of the tricuspid annular plane to the uppermost aspect of the RA wall) are ≤3.0 cm/m2 in men and ≤3.1 cm/m2 in women; for RA minor-axis dimension indexed to BSA (left-right, from the inter-atrial septum to the rightmost aspect of the RA wall), it is ≤2.5 cm/m2 in men and women.

RA volume — The RA tends to be slightly larger in men than in women even after indexing for BSA, and is slightly smaller than the LA (in part due to the method of measurement). RA volume can be measured by planimetry of the RA cavity in (a) single plane apical four chamber view at end-systole (when the RA cavity is at its largest) using the Simpson’s method, (b) two orthogonal views using the biplane ellipsoid method, or (c) 3D volume using the method of discs. The 2005 ASE/EACVI guidelines endorse the single plane Simpson’s method (a) with the normal reference limits being ≤39 mL/m2 in men and ≤33 mL/m2 in women .

Right ventricular size — RV enlargement may be caused by states of acute or chronic pressure overload, chronic volume overload, or intrinsic myocardial pathology, often indicating severe and/oradvanced disease with a relatively poor prognosis.

●In patients with moderate-to-severe chronic pulmonary disease, the basal diameter of the RV (measured at end-diastole and indexed to body surface area) was readily obtained in 92 percent of patients and was the most significant predictor of mortality over a follow-up period of 16 months .

●A large registry of patients presenting with acute pulmonary embolism demonstrated that relative RV enlargement, as suggested by an RV to LV end-diastolic diameter ratio ≥0.9, was predictive of in-hospital mortality and may be useful in identifying which patients require more aggressive therapy.

●For patients with repaired tetralogy of Fallot and residual-free pulmonary regurgitation, RV size is vigilantly monitored to determine the timing of pulmonary valve replacement. Although typically measured by magnetic resonance imaging (MRI) to achieve high accuracy  , reports suggest that 3D echocardiography provides similar measurements of RV volumes .

●Tricuspid regurgitation in the absence of organic tricuspid valve pathology, termed functional tricuspid regurgitation, is highly prevalent in patients with right heart disease, particularly those with chronic right ventricular pressure overload. RV enlargement, and more specifically, dilation of the basal annular portion of the RV, is one of the major causative factors.  

RV area — Due to the complex shape of the RV, there is no single representative 2D measure of RV size, and any given measure has modest correlation with actual RV volume as measured by MRI or ex vivo, especially when the RV cavity is dilated .

The area of the body and apex of the RV is measured by planimetry of the RV cavity in the apical four chamber view at end-diastole (when the RV cavity is at its largest).

The area of the body and apex of the right ventricle (RV, shown in yellow) is measured by planimetry of the ventricular cavity in the apical four chamber view at end-diastole. RV linear dimensions are also measured in the apical four chamber view, at both the basal (line 1) and mid (line 2) portions of the RV.

When tracing the endocardial contour, care must be taken to trace along the true border of the RV wall rather than the prominent trabeculations or moderator band . The normal reference limit for RV end-diastolic area is ≤24 cm2 in men and ≤20 cm2 in women.

Two common sources of error, resulting in underestimation of RV area, are:

●Tracing too far into the RV cavity along the border of the noncompacted RV trabeculations.

●Accidentally excluding the apex of the RV by tracing the inferior border along the moderator band rather than the true apex.

A. Proper tracing of the right ventricular (RV) endocardial outline.

B. Underestimation of RV size due to exclusion of noncompacted RV trabeculations.

C. Underestimation of RV size due to exclusion of the RV apex by incorrection tracing along the moderator band.

RV linear dimensions — RV linear dimensions are measured in the apical four chamber view, ideally using the RV-focused view, at end-diastole. The normal reference limits for RV basal dimension (maximal diameter in the basal one-third of the RV) and RV mid-cavity dimension (midway between the apex and annular plane) are ≤4.1 and ≤3.5 cm, respectively. The RV basal dimension is recommended as the preferred standard basic measure of RV size to be reported, unless 3D volumes are reported.

Two common sources of error with the measurement of RV linear dimensions are:

●Acquiring a non-optimized four chamber view that results in underestimation of RV size .

●Acquiring and making measurements on the RV-modified apical four chamber view (as opposed to the RV-focused apical four chamber view) that results in overestimation of RV size.

Diagram showing the recommended apical 4-chamber (A4C) view with focus on the right ventricle (RV) (1*) and the sensitivity of right ventricular size with angular change (2,3) despite similar size and appearance of the left ventricle (LV). The lines of intersection of the A4C planes (1*,2,3) with a mid left ventricular short-axis are shown above and corresponding A4C views below.

Therefore, it is critical to obtain a well-aligned RV-focused apical four chamber view. This is accomplished by ensuring that the transducer is positioned over the apex of the heart (and not over the body of the RV as in the RV-modified apical four chamber view), tilted to bring the entire RV into the imaging sector, and rotated until the maximal RV dimension is in-plane.

RVOT dimension — The proximal right ventricular outflow tract (RVOT) dimension is measured from the RVOT anteriorly to the aortic root posteriorly; it can be measured in the parasternal long-axis or parasternal short-axis view  and the normal reference limits are ≤3.3 and ≤3.5 cm, respectively. The distal RVOT diameter, commonly used in the calculation of RV stroke volume, is measured just proximal to the insertion of the pulmonary valve leaflets in the parasternal short-axis view  and the normal reference limit is ≤2.7 cm .

RV volume — Two-dimensional estimates of RV volume are not recommended due to their inherent geometric assumptions and lack of full representation of the different RV regions (often resulting in substantial underestimation of true RV volume). However, 3D measures of RV volume have largely overcome these limitations and can be obtained using one of two preferred approaches:

●Method of discs — Starting with a full volume acquisition of the RV, the user manually traces the endocardial border of the RV in a series of consecutive short-axis slices or orthogonal long-axis slices. The software algorithm segments the RV into contiguous discs of fixed height (usually 10 mm) from base to apex, and sums the volumes of the contiguous discs to calculate a global RV volume.

●3D surface modeling platforms — Also starting with a full volume acquisition of the RV, the user manually identifies specified RV landmarks or contours and the proprietary software algorithm proceeds to fit a 3D model and calculate global and regional RV volumes. The latter approach has become increasingly popular due to its ease and speed of use, close correlation with cardiac MRI, and availability of normative data in both men and women, as well as in younger and older adults. The normal reference limits for RV end-diastolic volume indexed to BSA are ≤87 mL/m2 in men and ≤74 ml/m2 in women.

Measurement of right ventricular outflow tract (RVOT) dimensions at the proximal or subvalvular level (RVOT-Prox) and at the distal or pulmonic valve (RVOT-Distal) in the (A) parasternal long-axis RVOT anterior portion view, (B) basal parasternal short-axis view, and (C) parasternal short-axis of pulmonary bifurcation view.

Of note, 3D measures of RV volume and ejection fraction are endorsed by the ASE/EACVI [5] in laboratories with suitable equipment and expertise and are supported by reference values obtained from a population of over 500 normal subjects .

Wall thickness — RV hypertrophy is recognized by inspecting the wall of the RVOT in the parasternal views, the RV free wall in the apical view, and the RV inferolateral/diaphragmatic wall in the subcostal view. Generally, the RV free wall in diastole is approximately 3 to 4 mm thick; if it exceeds 5 mm, it is considered hypertrophied.

Starting from a full-volume acquisition, the RV endocardial border is semi-automatically contoured in orthogonal planes (panels A, B, and C) and, using a surface modelling algorithm, a 3-dimensional volumetric representation of the RV is generated (panel D). Global and regional RV-end diastolic and end-systolic volumes are reported, along with RV ejection fraction.

RV wall thickness, when inspected or measured in the subcostal view, allows differentiation of the wall thickness from cavity trabeculations. Contrast enhancement of M-mode or two-dimensional images can aid in measuring wall thickness. Due to measurement variability, regardless of the method used, it should be noted that RV thickness by echocardiography has low sensitivity and specificity for identifying true RV hypertrophy.

INTERVENTRICULAR SEPTAL SHAPE — A D-shaped left ventricular cavity (also referred to as a flattened interventricular septum) in systole (particularly end-systole) suggests right ventricular (RV) pressure overload, whereas a D-shaped left ventricular cavity in diastole suggests RV volume overload.

The short axis view at the level of the mitral chordae from a patient with advanced pulmonary hypertension shows substantial morphologic changes, including severe hypertrophy of the right ventricular (RV) wall, dilation of the RV chamber and hypertrophy of the right side of the septum. The septum is flattened, strongly suggesting pressure overload in the RV; this septal shape imparts a "D shape" to the left ventricle (LV) which has relatively thin walls.

Serial stop-frame short-axis two-dimensional echocardiographic images of the left ventricle at the mitral chordal level with diagrams from a patient with isolated right ventricular (RV) pressure overload due to primary pulmonary hypertension (A) and from a patient with isolated RV volume overload due to tricuspid valve resection (B). Whereas the left ventricular (LV) cavity maintains a circular profile throughout the cardiac cycle in normal subjects, in RV pressure overload, there is leftward ventricular septal (VS) shift and reversal of septal curvature present throughout the cardiac cycle with most marked distortion of the left ventricle at end-systole. In the patient with RV volume overload, the septal shift and flattening of VS curvature occurs predominantly in mid to late diastole with relative sparing of LV deformation at end-systole.

A left ventricular eccentricity index (defined as the ratio of the length of two perpendicular minor-axis diameters, one of which bisects and is perpendicular to the interventricular septum) has been measured at end-diastole and end-systole to identify interventricular septal deformation in patients with RV volume and/or pressure overload.

RIGHT VENTRICULAR FUNCTION — The predominant motion of the right ventricle (RV) is longitudinal shortening, visible as systolic descent of the basal portion of the free wall toward the apex. A secondary motion is radial thickening, visible (albeit less readily) as systolic thickening of the myocardium. Unlike the left ventricle, circumferential shortening is negligible in the RV, owing to its lack of circumferential fibers. The quantitative echocardiographic parameters used to measure RV systolic function reflect longitudinal shortening, longitudinal shortening plus inwards motion, or global RV performance.

Tricuspid annular plane systolic excursion (TAPSE) — TAPSE, sometimes referred to as tricuspid annular motion (TAM), reflects longitudinal shortening of the RV. TAPSE is measured in the apical four chamber view by placing an M-mode cursor on the lateral tricuspid annulus and measuring the peak distance travelled by this reference point during systole.

Tricuspid annular plane systolic excursion (TAPSE) is measured in the apical four-chamber view by placing an M-mode cursor on the lateral tricuspid annulus and measuring the peak distance travelled by this reference point during systole. A greater distance travelled during systole implies greater right ventricular systolic function, with the normal reference limit being a TAPSE of ≥1.7 cm.

A greater distance travelled during systole implies greater RV systolic function, with the normal reference limit being a TAPSE of ≥1.7 cm.

The primary limitation of TAPSE is that it only represents one component of RV motion within one single segment of RV myocardium. The RV may be frankly dysfunctional despite relatively preserved TAPSE, as in some cases of severe pulmonary arterial hypertension. Alternatively, the RV function may be globally preserved despite significantly reduced TAPSE, as often seen after cardiac surgery.

Two common sources of error with TAPSE are:

●Not placing the M-mode cursor parallel to the plane of longitudinal motion, which results in angle-dependent underestimation of TAPSE.

●Incorrectly measuring the magnitude of displacement from the M-mode image.

These issues aside, TAPSE remains one of the most widely used measures of RV systolic function since it is easily obtained and has been shown to have robust diagnostic and prognostic value in several disease states.

●In patients with pre-capillary pulmonary hypertension, TAPSE has been shown to correlate well with MRI-derived RV ejection fraction and predict long-term mortality.

●In patients presenting with inferior myocardial infarction, a reduced TAPSE was found to be a rapid and accurate indicator of RV infarction even when no RV regional wall motion abnormalities could be identified .

●In three separate series of patients with chronic left-sided systolic heart failure, up to 50 percent of patients were found to have a reduced TAPSE, a finding that was associated with a significant increase in long-term mortality .

Tricuspid annular velocity (S’) — Akin to TAPSE that reflects the longitudinal displacement, S’ reflects the longitudinal velocity of the tricuspid annulus during systole. S’ is measured in the apical four chamber view by placing a tissue Doppler cursor on the lateral tricuspid annulus and measuring the peak velocity of this reference point during systole.

 

Care should be taken to measure the peak of the ejection waveform and not the earlier isovolumetric contraction waveform. A greater velocity during systole implies greater RV systolic function, with the normal reference limit being an S’ of ≥9.5 cm/s. Both pulsed tissue Doppler and color-coded tissue Doppler can be used to measure S’, although the color-coded method yields mean velocities that are usually slightly lower. The ultrasound transducer may be slightly tilted to optimize the alignment of the Doppler cursor with the plane of RV longitudinal motion.

The advantages and limitations are the same as TAPSE: S’ is simple to perform and has prognostic data, yet it is angle-dependent and only represents the longitudinal annular component of RV motion.

Like TAPSE, S’ appears to have prognostic value in a variety of clinical situations. S’ has been shown to correlate well with magnetic resonance imaging-derived (MRI) RV ejection fraction  and demonstrates prognostic value in patients with pulmonary hypertension, inferior myocardial infarction, chronic heart failure , and arrhythmogenic right ventricular cardiomyopathy.

Fractional area change (FAC) — FAC is the percent change in RV area from diastole to systole, a two-dimensional surrogate for ejection fraction, and thereby reflects the systolic function of the inflow and apical portions of the RV. FAC is not limited to one type of motion, but rather encompasses longitudinal shortening as well as radial thickening and the contribution of the interventricular septum. It is measured in the apical four chamber view by manually tracing the contour of the RV at end-diastole (when the RV cavity is at its largest) and at end-systole (when the RV cavity is at its smallest). The FAC is calculated as follows:

Examples of right ventricular fractional area change (FAC). Percentage FAC = 100 end-diastolic area (area ED) endsystolic area (area ES)/end-diastolic area. The endocardial border is traced in apical 4-chamber (A4C) views from the tricuspid annulus along the free wall to the apex, then back to the annulus, along the interventricular septum at end-diastole (ED) and end-systole (ES). Trabeculation, tricuspid leaflets, and chords are included in the chamber.

(A) Normal subject, FAC 60 percent.

(B) Moderately dilated right ventricle (RV), FAC 40 percent, and a markedly dilated left ventricle (LV).

(C) Dilated RV, FAC 20 percent, and the left ventricle (LV) is foreshortened as a result of optimizing the view for the right ventricular chamber.

●FAC = [(end-diastolic RV area – end-systolic RV area) / end-diastolic RV area] x 100

The normal reference limit  for FAC is ≥35 percent. The primary challenge and main limitation of FAC is the accurate identification and tracing of the true RV endocardial border rather than the prominent trabeculations and muscle bands.

FAC appears to be an excellent compromise between efficiency of use and global representation of RV systolic function. Compared to other two-dimensional measures of RV systolic function such as TAPSE and S’, FAC was found to correlate best with the reference standard of MRI-derived RV ejection fraction (R = 0.80) .

●In substudies from the SAVE and VALIANT trials, 416 and 522 patients with acute myocardial infarction and evidence of left ventricular dysfunction underwent complete echocardiographic assessment. Four independent predictors of subsequent all-cause mortality were identified: age, Killip classification, LV ejection fraction, and FAC; with FAC <35 percent carrying an adjusted hazard ratio of 3.56 (95% CI 1.07-11.90).

●In the Multidisciplinary Study of Right Ventricular Dysplasia, FAC was found to be significantly reduced in probands compared with normal controls. The revised arrhythmogenic right ventricular cardiomyopathy (ARVC) Task Force Criteria list FAC ≤33 percent as a major diagnostic criterion, and FAC 34 to 40 percent as a minor criterion (no other 2D echocardiographic measures of function were recommended)  

Myocardial performance index (MPI) — MPI, also referred to as right ventricular index of myocardial performance (RIMP) or right ventricular Tei index, reflects both the systolic and diastolic function of the RV . Contrary to the TAPSE, S’, and FAC, the MPI is based on time intervals and is independent of chamber geometry and contraction pattern. The MPI was once thought to also be independent of loading conditions, although this has been subsequently proven to be false.

The MPI is derived by calculating the ratio of isovolumetric time over ejection time as follows:

●MPI = (isovolumetric relaxation time + isovolumetric contraction time) / ejection time = (tricuspid closure-to-opening time – ejection time) / ejection time

Lower values indicate superior function since the healthy RV should theoretically spend a lower relative proportion of time in an isovolumetric state and a greater proportion ejecting blood.

The MPI can be measured in one of two ways . For both methods of measuring MPI, the expertise of the observer is crucial since the time intervals being measured are often difficult to delineate, and small variations can lead to substantial differences in the final calculated value.

Calculation of right ventricular myocardial performance index (MPI) pulsed tissue Doppler. The tricuspid (valve) closure opening time (TCO) encompasses isovolumic contraction time, ejection time (ET), and isovolumic relaxation time.

 

●Pulsed Doppler method – The ejection time is derived from the pulsed wave Doppler tracing of the distal RVOT; the tricuspid-closure-opening time is derived from the pulsed wave Doppler tracing of the tricuspid inflow (time from end of the A wave to the onset of the following E wave) or the continuous wave Doppler tracing of the tricuspid regurgitation jet; and the total isovolumetric time is derived from the difference between the tricuspid-closure-opening time and the ejection time. The normal reference limit for the pulsed Doppler MPI is ≤0.43.

●Tissue Doppler method – The ejection time, tricuspid-closure-opening time, and total isovolumetric time are all derived from the pulsed tissue Doppler tracing of the lateral tricuspid annulus. The normal reference limit for the tissue Doppler MPI is ≤0.54. This method has the distinct advantage of being measured from a single acquisition in a single heartbeat.  

MPI is particularly well suited to two clinical scenarios: First, since MPI is often affected before other functional parameters, it is a more sensitive parameter to evaluate subclinical or early RV dysfunction. Second, since MPI is non-geometric in nature and relies solely on time intervals to derive a measure of RV function, it is useful to evaluate an RV which is oddly shaped or poorly visualized.

Similar to TAPSE, S’, and FAC, MPI appears to have prognostic value in a variety of clinical conditions. Abnormal RV MPI has been linked to adverse outcomes in several disease states, and has been used to predict response to therapy in patients with pulmonary arterial hypertension and chronic thromboembolic disease.

RV ejection fraction by 3D — RVEF is calculated as ([end-diastolic volume – end-systolic volume] / end-diastolic RV volume), with volumes measured from a 3D acquisition. Given adequate image quality, 3D-derived RVEF using either the method of discs or surface modeling is the most accurate echocardiographic measure of RV systolic function. A study of 507 normal subjects has provided reference values for men and women. In general, the normal reference limit for 3D-derived RVEF is ≥45 percent.

Strain imaging by 2D — Strain is defined as the percent change in myocardial deformation (predominantly longitudinal shortening in the case of the RV), while its derivative strain rate is defined as the rate of myocardial deformation. These are measured using either a tissue Doppler (angle-dependent) or speckle tracking (non-angle-dependent) approach. Potential benefits include unique abilities to reflect the intrinsic contractility of the RV (with contractility defined as the stress-strain interplay), evaluate diastolic properties, perform regional analyses, and identify subclinical dysfunction. In addition to the paucity of normative and prognostic data, the major drawback limiting clinical applicability has been technical challenges in image acquisition and analysis (need for high frame rates, high signal-to-noise, minimal image dropout, experienced observers for reproducible measurements). Pooled data (though heavily weighted by a single vendor) suggest that global longitudinal RV free wall strain of magnitude less negative than -20 percent is likely abnormal.

Contemporary speckle-tracking algorithms have enhanced reproducibility and are beginning to yield clinically relevant observations.  One example of this is the use of free wall longitudinal strain by 2D speckle tracking to predict outcomes in a large cohort of patients with pulmonary arterial hypertension .

Diastolic function — Diastolic function of the RV, although infrequently considered, can be assessed by echocardiography in a fashion similar to the left ventricle using pulsed wave Doppler interrogation of the trans-tricuspid inflow, tissue Doppler interrogation of the lateral tricuspid annulus, and evaluation of RA pressure using inferior vena cava (IVC) size and collapsibility and hepatic vein flow pattern. A more detailed description of RV diastolic function assessment is included in the 2010 ASE right heart guidelines.

HEMODYNAMICS — In addition to the anatomic and functional parameters, the comprehensive echocardiographic examination provides an assessment of right heart hemodynamics. Integration of these three components (anatomy, function, and hemodynamics) is vital to enable the clinician to understand and delineate the pathophysiology at hand.

RA pressure — Estimation of right atrium pressure (RAP) is clinically relevant in many circumstances:

●As an indicator of volume status and responsiveness to fluid challenge in critically ill patients

●As a sensitive diagnostic sign in patients with suspected cardiac tamponade or other pericardial syndromes

●As part of the echocardiographic estimation of pulmonary artery pressure

RAP is determined based on the diameter and degree of collapse of the inferior vena cava (IVC) imaged from the subcostal view during quiet inspiration and during rapid inspiration (“sniff”)   Overly forceful inspiration should be discouraged, as this can cause translation of the IVC out of the imaging plane. RAP is typically estimated as follows:

●Normal RAP (3 mmHg): IVC diameter ≤2.1 cm and collapse during sniff >50 percent.

●Intermediate RAP (8 mmHg): IVC diameter ≤2.1 cm and collapse during sniff <50 percent or IVC diameter >2.1 cm and collapse during sniff >50 percent.

●Elevated RAP (15 mmHg): IVC diameter >2.1 cm and collapse during sniff <50 percent.

The interpreter, however, may upgrade or downgrade the intermediate RAP value based on secondary indices that suggest either normal or elevated RAP such as RA enlargement, RV hypertrophy, diastolic predominance in the hepatic veins, restrictive filling pattern in the trans-tricuspid inflow, or tricuspid E/e’ >6. In some subjects with markedly elevated RAP, the “elevated” category of 15 mmHg may be an underestimate, and this should be considered in certain clinical scenarios. In mechanical ventilated subjects, the use of IVC size and collapse to estimate RAP is less reliable, although this notion has been challenged. The use of the above algorithm is preferable over an assumed RAP of 5 or 10 mmHg for all patients.

The IVC is occasionally dilated in healthy young subjects and in athletes, in which case the IVC size can be reassessed in the left lateral decubitus position and ancillary signs of elevated RAP can be verified (hepatic vein flow pattern showing diastolic predominance, ie, diastolic wave velocity >systolic wave velocity). If the IVC appears plethoric and there is no suggestion of right heart pathology, positioning the patient in the left lateral decubitus position may cause the IVC to collapse normally with inspiration, and may be interpreted as normal RAP.

Pulmonary artery pressure

Estimation of pulmonary artery systolic pressure — Estimation of pulmonary artery pressure (PAP) is an important component of the echocardiographic study, particularly in the evaluation of dyspnea, and in patients with evidence of cardiac pathology. The simplified Bernoulli equation, ΔP = 4V2, estimates the pressure drop between two chambers (ΔP) based on the peak velocity (V) in the presence of turbulent flow. Thus, the gradient estimated by the peak tricuspid regurgitation velocity (TRV) measured by continuous wave Doppler is equal to the systolic pressure in the RV (RVSP) minus the systolic pressure in the RA (RAP). RVSP is equivalent to pulmonary artery systolic pressure (PASP) in the absence of a right ventricular outflow gradient (such as with pulmonic stenosis). This equation is re-arranged to yield:

●PASP ≈ RVSP = 4(peak TRV2) + RAP

Careful acquisition and interpretation of Doppler TRV and RAP data are required for accurate estimation of RVSP and PASP. While some studies have documented a strong correlation between echocardiographic estimates and right heart catheterization measurements of PASP  , other studies have found only a weak correlation. A cause of these discrepant findings is likely suboptimal Doppler TRV signal acquisition and interpretation. Of note, in a retrospective study including 307 echocardiograms in patients with advanced lung disease or pulmonary arterial hypertension, only 61 percent of studies included TR recordings deemed sufficient for an interpretation. When TR signal was interpretable, the area under the curve for classifying pulmonary hypertension was 0.97. When TR signals were uninterpretable, the left ventricular eccentricity index and right ventricular size were independently associated with pulmonary hypertension (area under the curve, 0.77).  

The following steps along with interpretation by an expert are suggested to optimize the accuracy of RVSP and PASP estimation:

●Examine the TR jet in multiple views (parasternal RV inflow, parasternal short-axis, RV-modified apical four-chamber, and subcostal views; the last particularly when the TR jet is highly medially directed) and measure the peak TRV using the Doppler spectral recording from the position most closely aligned with the jet. As with all Doppler measurements, it is critical to minimize the angle of incidence of the cursor to the flow (to <40°) to avoid underestimating TRV.

●Adjust the sweep speed between 75 and 150 mm/sec, depending upon the heart rate.

●When measuring peak TRV in a patient with an arrhythmia, avoid nonrepresentative beats. For example, avoid using a post-premature ventricular contraction beat. For patients with atrial fibrillation, use the third beat after two consecutive equal RR intervals.

●Optimize the signal-to-noise ratio by carefully adjusting the Doppler gain to avoid over- or underestimation of maximal velocities.

●Measure the peak TRV only if the signal is interpretable (with a complete or partial envelope).

●Measure the peak TR velocity using the modal frequency

●Use agitated saline contrast as needed to enhance the signal-to-noise ratio for the Doppler TR spectral recording.

●Integrate RA size, hepatic vein Doppler tracings, and tricuspid E/e’ along with IVC size and collapsibility to estimate RAP, and avoid translational motion when assessing the IVC.  

(A) Continuous wave Doppler showing tricuspid regurgitation (TR). Measurement of peak TR velocity should be performed at the modal frequency (point 1) rather than at the point of highest visible signs (point 2).

(B) Gain settings which are too low do not allow for appropriate visualization of the TR jet, leading to underestimation of the amount of TR and inability to accurately estimate pulmonary artery systolic pressure (PASP).

(C) PASP is estimated using the modified Bernoulli equation; PASP in the absence of right ventricular outflow obstruction is equivalent to right ventricular systolic pressure = right atrial pressure + [4 *(TR velocity)2].

In general, echocardiographically-estimated PASP exceeding 35 to 40 mmHg should be considered elevated, particularly in patients being evaluated for dyspnea. PASP rises slightly with increasing age and body surface area. While carefully performed echocardiographic estimation of PASP can provide helpful results, confirmation of PASP by invasive right heart catheterization is often indicated.

Other measures of pulmonary artery pressure — Echocardiography can also be used to estimate mean and diastolic pulmonary artery pressures, using either the tricuspid or pulmonary regurgitation velocity, or the acceleration time (time to reach peak velocity in the distal RVOT flow tracing measured by pulsed wave Doppler), as follows:

●Mean PAP = 4V2early PR velocity + RAP

●Mean PAP = 79 – [(0.45) (Acceleration time)]

●Mean PAP = VTI of the TR jet + RAP  

●Mean PAP = 0.61 x PASP + 2  

●Systolic PAP = 10[(-0.004)(Acceleration time) + 2.1] 

●Diastolic PAP = 4V2end PR velocity + RAP

These values may be reported in patients with right heart pathology, or may be used as surrogate measures of PAP when there is no adequate TR signal to estimate PASP. Furthermore, the combination of acceleration time ≤60 msec and PASP ≤60 mmHg, termed the 60/60 sign, has been proposed as an echocardiographic sign to identify patients with acute pulmonary embolism.

Pulmonary vascular resistance — The determinants of pressure are flow and resistance, according to the formula P = QR, where pressure (P) is equal to the product of flow (Q) and resistance (R). There are situations whereby stroke volume is markedly increased, without an increase in pulmonary vascular resistance (PVR). The PASP may therefore be elevated, but the pathological or clinical implications are not the same as in the setting of increased resistance. By using a measure of flow (velocity time integral [VTI] of the RVOT) and a measure of pressure (TRV), a simple regression formula can be used to estimate PVR:

PVR = [(TRV / RVOT VTI) x 10] + 0.16

This yields a value in Wood units (WU), and maintains a good correlation with invasively measured PVR up to approximately 8 WU. A subsequent refinement showed that PVR = (5.19 x TR Vmax2 / RVOT VTI) – 0.4 performed better, especially when PVR exceeded 6 WU. This measure has not been validated for clinical use or to prognosticate patients, and should not replace invasive hemodynamic measurements. It may be useful, however, to screen for pulmonary hypertension related to high flow states or in athletes, both at rest and with exercise. Of note, using the principles elaborated above, when the RV fails, and the stroke volume decreases, one may observe a fall in PASP

Other findings — There are several other ancillary findings that should be used to assess for RV overload. A D-shaped left ventricular cavity in systole suggests RV pressure overload. Mid-systolic notching of the RVOT pulsed wave Doppler flow signal or pulmonary valve M-mode signal suggests increased PVR . This finding reflects a prominent reflected wave, and has been used to refine estimates of PVR using the formula:

PVR = (PASP/ RVOT VTI) + 3 if a mid-systolic notching of the RVOT is present .

Systolic notching in the pulsed wave Doppler recording of right ventricular outflow tract flow. Mid-systolic notching strongly suggests elevated pulmonary vascular resistance.

In addition, when assessing for increased PAP or PVR, corroborative signs of right-sided dilation and dysfunction should be sought.

CONDITIONS ASSOCIATED WITH RIGHT VENTRICULAR PATHOLOGY — The right ventricle (RV) can be pathologically abnormal in response to a number of situations and conditions, many of which have characteristics that permit echocardiographic differentiation. RV pathology can be due to volume or pressure overload from a variety of etiologies (eg, valvular disease, congenital heart disease, etc). In addition, primary myopathic processes or tumors can result in RV pathology. Complete discussions of the following conditions are presented separately:

Conditions associated with RV volume overload

●Atrial septal defect  

●Valvular regurgitation (tricuspid or pulmonic regurgitation)  

Conditions associated with RV pressure overload

●Pulmonary arterial hypertension (idiopathic, heritable, drug-induced, HIV, connective tissue diseases)  

●Acute or chronic thromboembolic disease  

•Pulmonary hypertension due to left heart diseases (eg, systolic dysfunction, diastolic dysfunction, valvular heart disease).  

•Pulmonary hypertension due to lung diseases and/or hypoxemia.  

•Pulmonary valve or supra-valvular stenosis  

•RV outflow obstruction  

Cardiomyopathic conditions associated with RV pathology

●RV ischemia or infarction  

●Dilated cardiomyopathy  

●Arrhythmogenic RV cardiomyopathy  

●Endomyocardial fibrosis  

●Other cardiomyopathies affecting the RV and the left ventricle (eg, cardiac amyloidosis, stress-induced cardiomyopathy)  

Tumors involving the RV

●Cardiac myxomas  

●Other primary cardiac tumors (eg, sarcomas, fibromas, rhabdomyomas)  

●Metastatic lesions (eg, melanoma, renal cell carcinoma)  

SUMMARY AND RECOMMENDATIONS

●Assessment of the right heart is a critical component of every echocardiographic study. Measurement of chamber dimensions, evaluation of right ventricle (RV) systolic function, and estimation of hemodynamic parameters (eg, right atrial [RA] pressure, systolic pulmonary artery pressure [PASP]) should be routinely performed.

●When feasible, the following core measurements  should be reported in all studies (with additional measurements performed and reported as clinically indicated):

•RV basal diameter from the RV-focused apical four chamber view (normal ≤4.1 cm), or, if feasible, RV volume from a 3D acquisition.

•RA volume from the apical four chamber view using the single plane Simpson’s method.  

•RA pressure from the inferior vena cava (IVC) size and collapse (3, 8, 15 mmHg)  

•PASP from the tricuspid regurgitation (TR) velocity and estimated RA pressure  

•RV systolic function using at least one quantitative parameter: tricuspid annular plane systolic excursion (TAPSE; normal ≥1.7 cm), tricuspid annular velocity (S’) (normal ≥9.5 cm/s), fractional area change (FAC; normal ≥35 percent), myocardial performance index (MPI; normal ≤0.43 by pulsed Doppler or ≤0.55 by tissue Doppler). In addition, 3D-derived RVEF is recommended when suitable technology and expertise is available.